The research and development function of the MS Facility Core is to assist users with development of novel analytical methods. These generally relate to development of quantitative techniques to measure endogenous metabolites, development of methods to improve sample ionization and development of high performance UPLC methods. These internal projects are undertaken at no expense to users if they are intended to benefit a larger group of investigators and improve the technical skills of the facility core staff. The mission of the Mass Spectrometry (MS) Facility Core is to provide cost effective, state-of-the-art instrumentation and analytical expertise to Center Investigators and pilot and other supported projects in the P30 EHS Core Center This facility core is among the specialized service cores utilizing the technical personnel and instrument facilities located in the university-wide mass spectrometry facility and is used for identification, quantitation, and characterization of small molecule reaction products, e.g. eicosanoids and oxidized lipids (1-3), DNA base adducts (4-7), identification and characterization of modified oligonucleotides (8-10), and metabolic activation of xenobiotic toxicants (1, 11-13).